The present invention is directed to an improved hydrogen vent assembly for use on chlor-alkali diaphragm cells. The entire assembly is fabricated from a polymeric material, preferably in one-piece blow molding operation. The assembly can be used on either existing cells as a replacement part or on new cells.
Conventional diaphragm cells used in the chlor-alkali industry generate chlorine and sodium hydroxide as principle electrochemical products from the electrolysis of brine. Such cells contain a plurality of anode and cathode chambers where the chlorine and sodium hydroxide, respectively, are produced. A small but none the less significant amount of hydrogen is also formed in the cathode chamber. The hydrogen gas is usually collected by means of overhead piping and stored in a container for disposal. During the operation of the cell, hydrogen can build up within the cathode chamber, and if such build-up is not controlled, it can damage internal cell components or even lead to explosions within the cell. As a safety feature, many commercial cells now in use, such as the H-4 cell manufactured by the Occidental Chemical Corporation, are equipped with a device for venting excess hydrogen from the cell in the event that the hydrogen pressure exceeds a designated level. Conventional hydrogen vent assemblies are fabricated from a complex network of iron or steel piping and are attached to the upper external surface of the cell. One end of the assembly communicates with the interior of the cell through an opening provided in the upper external portion of the cell. This opening collects hydrogen from the individual cathode compartments of the cell. The assembly is provided with a cup for containing water as a pressure regulator, and a manometer for measuring pressure. If the hydrogen pressure in the cell exceeds the level of water in the cup, the hydrogen gas bubbles through the vent and is safely discharged into the atmosphere.
Although the conventional hydrogen vent assembly is fabricated largely from standard metal components, it suffers from a number of serious drawbacks. Since the assembly is fabricated entirely of iron or steel, it tends to rust prematurely and must therefore be frequently replaced. Once installed, the assembly cannot be easily repaired or replaced which creates maintenance and reinstallation problems. In addition, the conventional design provides for a relatively low seal level relative to the cell which increases the risk of overflow of corrosive catholyte liquor through the vent during cell start-up. This can pose a significant safety hazard since the cells are periodically shut down and restarted under normal operation conditions.
It is therefore the principle object of the present invention to provide an improved hydrogen vent assembly which successfully overcomes the numerous disadvantages associated with the vent assemblies of the prior art.